Medical research has demonstrated the importance of maintaining adequate hydration while engaging in strenuous physical activities, such as running, bicycling, hiking, or mountain climbing. In the not too distant past, participants in such activities carried their water in bottles or canteens from which they drank periodically. More recently, personal hydration systems have been developed which allow users to drink more or less continuously while engaged in sporting or recreational activities. These personal hydration systems typically have a bag-like fluid reservoir that is carried in a back- or waist-mounted pack. A long flexible tube is connected to the reservoir through an exit port at one end and terminates in a mouthpiece at the other end. The tube is long enough to allow the mouthpiece to be carried in the user's mouth to enable the user to draw water from the reservoir at will. Examples of hydration systems and mouthpieces therefor are disclosed in U.S. Pat. Nos. 5,727,714, 5,060,833, 5,085,349, and 6,070,767, the disclosures of which are hereby incorporated by reference.
Although personal hydration systems have proven to be a great advance over traditional water bottles, they do suffer from some drawbacks. One such drawback is providing a fluid reservoir with an interior that may be readily accessed by the user, such as for cleaning. Fluid reservoirs for hydration systems typically include a sealable opening through which a volume of fluid is added to the reservoir. An example of such an opening is a narrow-diameter neck that is sealed through a friction fit with a cap. Another example is a reservoir with an opening defined by generally opposed ribs that are sealed by compressing the ribs against each other, much like a ZIPLOCK™ brand storage bag. Still another example is a roll top, or folded, opening, much like a dry bag used in camping. These designs suffer from limitations regarding either their accessibility to the interior of the reservoir, or their durability, such as when exposed to repeated opening and closing and to external forces.